Tissue-specific and pretranslational character of variants of the rosy locus control element in Drosophila melanogaster

Meiotic gene conversion tract length distribution within the rosy locus of Drosophila melanogaster

Employing extensive co-conversion data for selected and unselected sites of known molecular location in the rosy locus of Drosophila. we determine the parameters of meiotic gene conversion tract length distribution. The tract length distribution for gene conversion events can be approximated by the equation P(L > or = n) = phi n where P is the probability that tract length (L) is greater than or equal to a specified number of nucleotides (n). From the co-conversion data, a maximum likelihood estimate with standard error for phi is 0.99717 +/- 0.00026, corresponding to a mean conversion tract length of 352 base pairs. (Thus, gene conversion tract lengths are sufficiently small to allow for extensive shuffling of DNA sequence polymorphisms within a gene). For selected site conversions there is a bias towards recovery of longer tracts. The distribution of conversion tract lengths associated with selected sites can be approximated by the equation P(L > or = n/ selected) = phi n(1 - n + n/phi), where P is now the probability that a selected site tract length (L) is greater than or equal to a specified number of nucleotides (n). For the optimal value of phi determined from the co-conversion analysis, the mean conversion tract length for selected sites is 706 base pairs. We discuss, in the light of this and other studies, the relationship between meiotic gene conversion and P element excision induced gap repair and determine that they are distinct processes defined by different parameters and, possibly, mechanisms.

The rosy locus in Drosophila melanogaster: xanthine dehydrogenase and eye pigments

The rosy gene in Drosophila melanogaster codes for the enzyme xanthine dehydrogenase (XDH). Mutants that have no enzyme activity are characterized by a brownish eye color phenotype reflecting a deficiency in the red eye pigment. Xanthine dehydrogenase is not synthesized in the eye, but rather is transported there. The present report describes the ultrastructural localization of XDH in the Drosophila eye. Three lines of evidence are presented demonstrating that XDH is sequestered within specific vacuoles, the type II pigment granules. Histochemical and antibody staining of frozen sections, as well as thin layer chromatography studies of several adult genotypes serve to examine some of the factors and genic interactions that may be involved in transport of XDH, and in eye pigment formation. While a specific function for XDH in the synthesis of the red, pteridine eye pigments remains unknown, these studies present evidence that: (1) the incorporation of XDH into the pigment granules requires specific interaction between a normal XDH molecule and one or more transport proteins; (2) the structural integrity of the pigment granule itself is dependent upon the presence of a normal balance of eye pigments, a notion advanced earlier.

The l(3)S12 locus of Drosophila melanogaster: heterochromatic position effects and stage-specific misexpression of the gene in P element transposons

l(3)S12 is a vital locus whose function is required in embryos, early larvae, late pupae and oogenesis. We have identified a cold-sensitive allele, l(3)S12(3), and characterized conditional misexpression of the gene associated with this mutation as well as with several euchromatic insertions of l(3)S12+ transposons. Surviving cold-sensitive mutants as well as underexpression variants generated by P element transformation display a phenotypic syndrome that can include delayed development, abnormal bristle morphology, and female sterility. Using these phenotypes, defects in putative "early" and "late" l(3)S12 expression can be identified. The sensitivity of certain l(3)S12+ insertions to site-specific euchromatic position effect appears to be due to separation of the gene from an endogenous enhancer element during cloning. This enhancerless construct can be used to identify and perhaps to select "permissive" euchromatic sites, presumably adjacent to enhancer elements, which in some cases permit elevated production not only of the l(3)S12 message, but also of a P element-l(3)S12 fusion transcript. Certain of these permissive sites appear to control stage-specific expression, and we propose that this system may be used to identify, clone, and characterize such loci. Heterochromatic position effect on this locus has been demonstrated. Available evidence suggests that the l(3)S12 gene may be involved in protein synthesis, perhaps encoding a ribosomal protein.

Inter-species complementation of a rosy deficiency in Drosophila melanogaster

A chimeric Xdh gene was constructed in vitro, by recombining DNA sequences from the Dipterans Drosophila melanogaster and Calliphora vicina. The ry506 strain, an eye-colour mutant of Drosophila that is deficient for Xdh, was genetically transformed with the recombinant gene. Transformed flies with ry+ eye phenotype and increased resistance to purine were obtained, showing that the chimeric XDH is physiologically active in Drosophila. XDH activity was detected in crude extracts from transformed flies, yet at lower levels than in wild-type controls. The amounts of Xdh transcripts in the transformants were found to be 8 to 16% of the amount of wild-type ry mRNA, suggesting that Calliphora Xdh sequences may be relatively inefficient for mRNA production in Drosophila, or may produce unstable mRNA.

Xanthine dehydrogenase is transported to the Drosophila eye

The rosy (ry) locus in Drosophila melanogaster codes for the enzyme xanthine dehydrogenase. Mutants that have no enzyme activity are characterized by a brownish eye color phenotype reflecting a deficiency in the red eye pigment. This report demonstrates that enzyme which is synthesized in some tissue other than the eye is transported and sequestered at the eye. Previous studies find that no leader sequence is associated with this molecule but a peroxisomal targeting sequence has been noted, and the enzyme has been localized to peroxisomes. This represents a rare example of an enzyme involved in intermediary metabolism being transported from one tissue to another and may also be the first example of a peroxisomal protein being secreted from a cell.

Spatial regulation of zerknüllt: a dorsal-ventral patterning gene in Drosophila

zerknüllt (zen) is one of approximately 10 zygotically active genes that control the differentiation of the dorsal-ventral (D/V) pattern during early embryogenesis in Drosophila. Past genetic analyses suggest that maternal factors repress the expression of zen in ventral regions, thereby restricting zen products to dorsal and dorsal-lateral regions of precellular embryos. Subsequent interactions with other zygotic D/V regulatory genes refine the zen pattern, restricting expression to the dorsal-most ectoderm. Here we describe the use of zen promoter fusions and P-element transformation to identify cis elements that are responsible for the complex spatial pattern of zen expression. The zen promoter shows a two-tier organization: Distal sequences mediate its initial response to maternal factors, whereas proximal sequences are responsible for the refinement of the pattern in older embryos. The distal regulatory element has the property of a silencer (or anti-enhancer) element and can act over a distance to repress ventral expression of a heterologous promoter. Also, we discuss evidence that proximal promoter sequences interact with factors that may be modulated by a cell-cell communication pathway.

Molecular analysis of recombination events in Drosophila

The locations of crossover junctions and gene conversion tracts, isolated in the rosy gene of Drosophila melanogaster, were determined using DNA sequencing and denaturing gradient gel electrophoresis. Frequent DNA sequence polymorphisms between the parental genes served as unselected genetic markers. All conversion tracts were continuous, and half of the reciprocal crossover events had conversion tracts at the crossover junction. These experiments have also identified the sequence polymorphisms responsible for altered gene expression in two naturally occurring rosy variants.

Recombination can initiate and terminate at a large number of sites within the rosy locus of Drosophila melanogaster

This report presents the results of a recombination experiment designed to question the existence of special sites for the initiation or termination of a recombination heteroduplex within the region of the rosy locus. Intragenic recombination events were monitored between two physically separated rosy mutant alleles ry301 and ry2 utilizing DNA restriction site polymorphisms as genetic markers. Both ry301 and ry2 are known from previous studies to be associated with gene conversion frequencies an order of magnitude lower than single site mutations. The mutations are associated with large, well defined insertions located as internal sites within the locus in prior intragenic mapping studies. On the molecular map, they represent large insertions approximately 2.7 kb apart in the second and third exons, respectively, of the XDH coding region. The present study monitors intragenic recombination in a mutant heterozygous genotype in which DNA homology is disrupted by these large discontinuities, greater than the region of DNA homology and flanking both sides of the locus. If initiation/or termination requires separate sites at either end of the locus, then intragenic recombination within the rosy locus of the heterozygote should be eliminated. Contrary to expectation, significant recombination between these sites is seen.

Mutations affecting expression of the rosy locus in Drosophila melanogaster

The rosy locus in Drosophila melanogaster codes for the enzyme xanthine dehydrogenase (XDH). Previous studies defined a "control element" near the 5' end of the gene, where variant sites affected the amount of rosy mRNA and protein produced. We have determined the DNA sequence of this region from both genomic and cDNA clones, and from the ry+10 underproducer strain. This variant strain had many sequence differences, so that the site of the regulatory change could not be fixed. A mutagenesis was also undertaken to isolate new regulatory mutations. We induced 376 new mutations with 1-ethyl-1-nitrosourea (ENU) and screened them to isolate those that reduced the amount of XDH protein produced, but did not change the properties of the enzyme. Genetic mapping was used to find mutations located near the 5' end of the gene. DNA from each of seven mutants was cloned and sequenced through the 5' region. Mutant base changes were identified in all seven; they appear to affect splicing and translation of the rosy mRNA. In a related study (T. P. Keith et al. 1987), the genomic and cDNA sequences are extended through the 3' end of the gene; the combined sequences define the processing pattern of the rosy transcript and predict the amino acid sequence of XDH.

Sequence of the structural gene for xanthine dehydrogenase (rosy locus) in Drosophila melanogaster

We determined the nucleotide sequence of a 4.6-kb EcoRI fragment containing 70% of the rosy locus. In combination with information on the 5' sequence, the gene has been sequenced in entirety. rosy cDNAs have been isolated and intron/exon boundaries have been determined. We find an open reading frame which spans four exons and would encode a protein of 1335 amino acids. The molecular weight of the encoded protein (xanthine dehydrogenase), based on the amino acid translation, is 146,898 daltons which agrees well with earlier biophysical estimates. Characteristics of the protein are discussed.

DdcDE1, a mutant differentially affecting both stage and tissue specific expression of dopa decarboxylase in Drosophila

The isolation and characterization of a unique Dopa decarboxylase (Ddc) mutant in Drosophila melanogaster is reported. This mutant, DdcDE1, exhibits stage- and tissue-specific altered Ddc expression. Homozygous DdcDE1 embryos, central nervous systems (CNSs) at pupariation and newly eclosed adult epidermis all have approximately 5% as much specific dopa decarboxylase (DDC) activity as the pr control stock in which DdcDE1 was induced. In contrast, the DdcDE1 epidermis at pupariation has roughly 50% as much DDC activity as controls, a 10-fold increase over the relative activity detected in other tissues and stages. Although the adult cuticle lacks proper pigmentation as expected in flies with low DDC activity (less than or equal to 5%), the bristles unexpectedly have wild-type black pigmentation. This implies that the bristle forming cells have more DDC activity than the rest of the adult epidermis. This variegated phenotype, black bristles and pale cuticle, plus the fact that DdcDE1 was originally isolated in a reciprocal translocation between proximal X heterochromatin and the euchromatic left arm of the second chromosome, 42 bands from the Ddc locus, suggested that the mutant might be an example of position-effect variegation. All tests for position-effect variegation, including persistence of the mutant phenotype when DdcDE1 was removed from the translocation, were negative. At pupariation DDC cross-reacting material (CRM) levels are similar in DdcDE1 and wild-type controls, but in newly eclosed adults CRM levels are approximately 35% of wild-type controls. This suggests that DDC produced by DdcDE1 adults has less activity per DDC molecule than the DDC produced at pupariation by DdcDE1. If the DDC enzyme produced by DdcDE1 at adult eclosion had full DDC activity (35% DDC CRM = 35% DDC activity) then no mutant phenotype would be exhibited by DdcDE1 since flies with as little as 10% activity have a wild-type phenotype. DDC thermolability assays clearly demonstrate that DDC from DdcDE1 is more thermolabile than control DDC at both pupariation and adult eclosion. Furthermore, DDC from adults in both DdcDE1 and the pr control is more thermolabile than DDC from white prepupae. Mixing experiments indicate the difference in DDC thermolability between pr white prepupae and pr adults is not due to a difference in the white prepupal and adult supernatants. This suggests that in wild-type different isoforms of DDC are produced either by differences in post-translational modification or as a result of a different primary amino acid sequence.(ABSTRACT TRUNCATED AT 400 WORDS)

The inheritance of a urease-null trait in soybeans

Four soybean seed urease nulls (lacking both the activity and antigen of the embryo-specific urease) were intermated and the F1 and F2 seed examined for urease activity. Both generations were without urease activity, and the nulls were therefore considered noncomplementing. In crosses of each null line to cultivars homozygous for the allelic, codominantly inherited urease slow or fast isozyme, the F1 seed expressed the embryo-specific urease isozyme of the urease-expressing parent. A 3 ∶ 1 segregation for presence and absence of urease was observed in progeny from F1 and heterozygous F2 plants. The F2 and F3 from fastXnull combinations revealed that urease-positive seed were all phenotypically urease fast, while the same seed from slowXnull combinations showed a segregation of one seed containing a fast urease, either exclusively or in a heterozygous state with the slow isozyme, for every 69 phenotypic slows. Data pooled from F2 plants which segregate for both the presence (Sun) and absence (Sun) of urease and for the fast (Eu1-b) or slow (Eu1-a) urease allele indicate that the null lesion (Sun) is linked to Eu1 by approximately one map unit. The evidence is consistent with two models: (1) sun is an allele at the embryo-specific urease isozyme locus (Eu1) and that a high degree of exchange (and/or conversion) within the locus results in a 1% recombination frequency between the null trait and urease allozyme; (2) sun is at a distinct locus which is separated by one map unit from the embryo-specific urease isozyme locus (Eu1) upon which it acts in the cis position. Polyadenylated embryo RNA from one of the null lines, PI 229324, exhibited no urease template activity in vitro. Thus, the lack of urease antigen is due to lack of accumulation of translatable urease mRNA. The availability of soybeans lacking seed urease should be extremely useful to breeders as a trait for linkage studies and to geneticists as a transformation marker.

Studies of normal and position-affected expression of rosy region genes in Drosophila melanogaster

Transformant complementation, intragenic deletions and Northern blot analyses provide unambiguous localization of the l(3)S12 gene immediately proximal to the 5' end of the rosy locus. We have characterized an array of transformants with respect to l(3)S12 and rosy expression. The l(3)S12 gene is exceedingly sensitive to euchromatic site-specific position effects. Unlike the rosy locus, l(3)S12 is insensitive to heterochromatic position effect in rearrangements, as well as in a transformant located in heterochromatin. Cotransformants for both l(3)S12 and rosy elicit no apparent pattern of concordance with respect to euchromatic site-specific position effects. Heterochromatic-euchromatic rearrangements are examined with respect to position effects on expression of the rosy region genes l(3)12, rosy, snake and piccolo, as well as suppressor effects. Clear distinction is seen between euchromatic and heterochromatic effects.

Genetic and developmental characterization of the aldox-2 locus of Drosophila melanogaster

The aldox-2 locus in Drosophila melanogaster has been shown to affect differentially three molybdoenzymes, aldehyde oxidase, pyridoxal oxidase, and xanthine dehydrogenase. These effects are most obvious at times surrounding the pupal-adult boundary, when the normal organism accumulates large amounts of these enzymes in their active form. This locus has been more precisely mapped genetically to 2-82.9 +/- 2.1, with complete concordance between the effects of all recombinant chromosomes on all three enzymes. The cytogenetic location has also been determined to be between 52E and 54E8, with the likelihood that it lies within the region 54B1-54E8. The aldox-2 mutant allele has no visible phenotype and is completely recessive for enzyme effects at all stages tested. Segmental duplication of this region, including the aldox-2+ allele, has no apparent effect on the visible phenotype or the enzymatic activity. The mutant aldox-2 allele has no effect on the developmental expression of two unrelated enzymes, 6-phosphogluconate dehydrogenase and NADP+-dependent isocitrate dehydrogenase. The effects of this locus on aldehyde oxidase, xanthine dehydrogenase, and pyridoxal oxidase suggest that this locus may code for a product involved in the synthesis of the molybdenum cofactor common to these enzymes.

The underlying bases of gene expression differences in stable transformants of the rosy locus in Drosophila melanogaster

This report represents a continuation of our laboratory's effort to understand the major phenomena associated with P-M dysgenesis-mediated transformation in Drosophila. A group of stable transformants are characterized with respect to rosy gene expression. Stable, true-breeding, line-specific variants in gene expression are described. These are shown to be associated with single transposons present in each line, and the lines are free of functional P elements. The effects on expression are cis-acting, and there are no identifiable rosy DNA sequence lesions associated with these transposons. Evidence is presented that demonstrates that two features of the transformation experimental system are responsible for such variation. The first relates to the fact that the transposons insert at numerous genomic sites. Both heterochromatic and euchromatic position effects are characterized. The second relates to the fact that transformation involves dysgenic mobilization of a P-element transposon. This process is mutagenic, and such a mutation is characterized.

Molecular mapping of the rosy locus in Drosophila melanogaster

The DNA from the chromosomal region of the Drosophila rosy locus has been examined in 83 rosy mutant strains. Several spontaneous and radiation-induced alleles were associated with insertions and deletions, respectively. The lesions are clustered in a 4-kb region. Some of the alleles identified on the DNA map have been located on the genetic map by fine-structure recombination experiments. The genetic and molecular maps are collinear, and the alignment identifies the DNA location of the rosy control region. A rosy RNA of 4.5 kb has been identified; its 5' end lies in or near the control region.

Genetic analysis of the right (3') end of the rosy locus in Drosophila melanogaster

Prior reports from this laboratory have described the experimental basis for our understanding of the rosy locus (ry: 3–52·0) ofDrosophila melanogasteras a bipartite genetic entity consisting of a structural element that codes for the xanthine dehydrogenase (XDH) peptide and a contiguouscis-acting control element immediately to the left of the structural element. Although the left end (5′) of the structural element has been well defined, the right boundary (3′) has been given only casual treatment in our prior reports. In our recent studies of rosy locus expression we have been concerned with the production and identification of mutations in the non-structural regions immediately flanking the structural element. An improved definition of the right end of the structural element is essential to this analysis. In addition to producing a better definition of the right boundary of the structural element, this study produced several phenotypically novel mutations. These mutations were classified initially ascontrol element mutations, but upon analysis were found to map within the rosy structural element.Noevidence was obtained for the existence of a control element contiguous with the right end of the structural element.

On the identification of the rosy locus DNA in Drosophila melanogaster: intragenic recombination mapping of mutations associated with insertions and deletions

DNA extracts of several rosy-mutation-bearing strains were associated with large insertions and deletions in a defined region of the molecular map believed to include the rosy locus DNA. Large-scale, intragenic mapping experiments were carried out that localized these mutations within the boundaries of the previously defined rosy locus structural element. Molecular characterization of the wild-type recombinants provides conclusive evidence that the rosy locus DNA is localized to the DNA segment marked by these lesions. One of the mutations, ry2101, arose from a P-M hybrid dysgenesis experiment and is associated with a copia insertion. Experiments are described which suggest that copia mobilizes in response to P-M hybrid dysgenesis. Relevance of the data to recombination in higher organisms is considered.

Dysgenesis-induced instability of rosy locus transformation in Drosophila melanogaster: analysis of excision events and the selective recovery of control element deletions

Utilizing the method of P-M hybrid dysgenesis-mediated gene transfer to insert rosy locus DNA into various chromosomal locations, we recovered a transformed strain that carries an ry+ transposon inserted in or near the scalloped locus in polytene section 13F on the X chromosome. The resultant product, when stabilized, behaves as a homozygous and hemizygous viable and fertile extreme scalloped allele associated with wild-type expression of the rosy locus. We have labeled this allele, sdry+. This allele has been destabilized by subsequent P-M hybrid dysgenesis, and mutations were recovered that exhibit alterations in the rosy and/or scalloped phenotypes. Representative samples of all phenotypic classes have been characterized by Southern blot analyses of restricted DNA. The most common events are excisions of DNA wholly internal to the transposon and representing sections of rosy DNA. In addition to loss of rosy locus function, such excisions affect the scalloped locus expression.--A second dysgenesis experiment was carried out involving an ry+ transposon inserted in polytene section 16D on the X chromosome. A minimal estimate of the relative frequency of imprecise excisions, determined in this experiment is 75%.--A successful pilot experiment is described that utilizes dysgenic perturbation of the sdry+ allele to select for small deletions of the 5' noncoding region of the rosy locus.

A selective screen for transposable element mobilization in Drosophila melanogaster

A selective system is described that provides a simple and sensitive assay for the detection and analysis of induced mobile element transpositions in Drosophila melanogaster. The system will detect a single event in samples greater than 10(6) and thus provides a eucaryotic assay system for monitoring the induction of transposition by a variety of agents including, but not limited to, chemical carcinogens and toxins, ionizing radiation, and various environmental pollutants. The experimental system focuses on an X-linked rosy+ transposon and a conditional lethal system that permits the detection of a single transposition event in very large samples. The results of a pilot experiment utilizing this system are presented.